Xia X, Rocha P S, Selvaraj G, Bertrand H
Department of Microbiology, University of Guelph, ON, Canada.
Plant Mol Biol. 1994 Nov;26(3):817-32. doi: 10.1007/BF00028851.
Canrep is a heterogeneous, tandemly repeated, 176 bp nucleotide sequence that contains a single Hind III site and is present in high copy numbers in the genomes of many Brassica species. Complete clusters of repeats of this DNA were cloned from the nuclear DNA of Brassica juncea. Restriction-fragment dimers and higher multimers of the 176 bp sequence have arisen by mutations within the Hind III recognition sequence. Adjacent repeats from within the same cluster usually have different nucleotide sequences with features indicating that diversity is generated by a mechanism that causes site-specific base substitutions. While most of the units of canrep DNA are clustered in long arrays of tandem repeats, some are dispersed throughout the genome as isolated copies or in small clusters. Regardless of the size of the arrays, each cluster begins and ends with a variable-length, truncated repeat and is flanked by inverted copies of the sequence 5'-ATCTCAT3'-, which is not part of the basic sequence of the canrep family of DNAs. Furthermore, some clusters are located close to nucleotide sequences related to those of known plant transposons. Thus, canrep elements may be dispersed by transposition. There are two distinct subfamilies of canrep sequences in B. juncea, and one of these is closely related to one of the two subfamilies of this type of DNA from B. napus, indicating that it originated from B. campestris, the common diploid ancestor of both amphidiploid species. Neither the repetitive DNA nor nucleotide sequences flanking canrep clusters are transcribed in seedlings, suggesting that even small arrays of repeats are located in heterochromatic regions and might be involved in chromatin condensation and/or chromosome segregation.
Canrep是一种异质的、串联重复的176bp核苷酸序列，它含有一个单一的Hind III位点，并且在许多芸苔属物种的基因组中以高拷贝数存在。从芥菜型油菜的核DNA中克隆出了这种DNA的完整重复簇。176bp序列的限制性片段二聚体和更高的多聚体是由Hind III识别序列内的突变产生的。同一簇内相邻的重复序列通常具有不同的核苷酸序列，其特征表明多样性是由一种导致位点特异性碱基替换的机制产生的。虽然大多数Canrep DNA单元聚集在串联重复的长阵列中，但有些则作为孤立的拷贝或小簇分散在整个基因组中。无论阵列大小如何，每个簇都以可变长度的截短重复序列开始和结束，并由序列5'-ATCTCAT3'-的反向拷贝侧翼，该序列不是Canrep家族DNA基本序列的一部分。此外，一些簇位于与已知植物转座子相关的核苷酸序列附近。因此，Canrep元件可能通过转座作用而分散。芥菜型油菜中有两个不同的Canrep序列亚家族，其中一个与甘蓝型油菜这种类型DNA的两个亚家族之一密切相关，这表明它起源于这两个双二倍体物种的共同二倍体祖先油菜。Canrep簇侧翼的重复DNA和核苷酸序列在幼苗中均不转录，这表明即使是小的重复阵列也位于异染色质区域，可能参与染色质凝聚和/或染色体分离。
